I am part of a co-operative in central Australia. We have a property south of Alice Springs with 700 mature date palms. The orchard is currently being watered by a central bore with a standing height of water at 40m. Its a shaft driven Mono running off a Hino diesel engine. The absorbed power at 1200rpm is around 11kw. We need to plan to be able to pump at least 250kL a day.We also have a 3kW cool room that we have been running from a small honda generator for a few months of the year. Obviously all of this should not continue:)We started out planning a staged approach to getting on solar. Just a large PV array coupled to a three phase motor via a DC-to-variable frequency AC controller/inverter. And leave the coolroom till later. We are now leaning towards doing the whole lot at the same time with a big off grid system. We have had a quote for around 20kw of PV, AC coupled to three phase SMA island and a 48v 1660Ah gel bank.A VSD would drive a three phase motor, that would be triggered to switch on and off according to a preset SOC.

There are many ways to to skin this cat, and Im open to any and all suggestions about alternatives. I do have a couple of particular thoughts/issues.

1- Unlike coupling the PV direct to the motor with controller that can vary the speed of the pump (which is positive displacement) to match the incoming PV. Running it directly from the off grid inverters and battery bank according to State of Charge seems like it could unnecessarily cycle the batteries, when we are in fact extremely flexible about when we actually deliver the water. ie if we get a a cloud or a cloudy day then pump will be drawing from the batteries to run flat out, then stop, wait untill the batteries are recharged, then start again. This could go on many times a day, rather then throttling the motor down to match the PV input.

2-I've been running some small LiFePO4 battery banks, 12, 24, and 48v. I am super impressed with there performance and I cant personally imaging dropping big dough on lead at this stage of the precedings. I have been following all the discussion here and a fare bit elsewhere on the reality's of managing off-grid Lithium, and it seems that the numbers stack up well in its favour. I certainly have no problem advocating for it on a smaller scale, but at this size it starts to get pretty expensive. Not to mention that the installer would take no responsibility for the batteries.How should I put this to the group? We can decide either way. I'm really keen to move away from lead acid (which im also quite familiar with) but i would basically be taking responsibility for managing the battery bank. Also what size would you advocate for?

I'm acutely aware of how illogical it is to run large cooling loads from batteries, and I'm in the process of working up a design along the lines of http://pcpaustralia.com.au/pcm-applications/cold-storage/, but this might take a little while. Dates arnt that sensitive and we have up until now only run the cool room during the day anyway. So I'm not really counting on the batteries to supply guaranteed power for the cool room all day every day.

gfsben wrote:I am part of a co-operative in central Australia. We have a property south of Alice Springs with 700 mature date palms. The orchard is currently being watered by a central bore with a standing height of water at 40m. Its a shaft driven Mono running off a Hino diesel engine. The absorbed power at 1200rpm is around 11kw. We need to plan to be able to pump at least 250kL a day.

running this direct from Solar is more effective than just about any other way there is, doing it from batteries is not a good use of any battery technology.

gfsben wrote:We also have a 3kW cool room that we have been running from a small honda generator for a few months of the year. Obviously all of this should not continue:)

There is a solution to this which uses a combinations of technologies but allows for 24 x 7 cooling. Which is perfectly viable for off-grid (my design), demand for power during the night is very low. The cost of course depends on how big the cool room is, how well insulted it is and how cold you want it.

gfsben wrote:There are many ways to to skin this cat, and Im open to any and all suggestions about alternatives. I do have a couple of particular thoughts/issues.

There are, but some work really well and are much better choices compared to others, more reliable lower maintenance, etc.

gfsben wrote:1- Unlike coupling the PV direct to the motor with controller that can vary the speed of the pump (which is positive displacement) to match the incoming PV. Running it directly from the off grid inverters and battery bank according to State of Charge seems like it could unnecessarily cycle the batteries.

Not an efficient use equipment resources, direct PV is far less prone to failure and the longevity is far, far better, although generally the pumps we've used are different.

Ben wrote:I'm acutely aware of how illogical it is to run large cooling loads from batteries...

I wish you'd told me that a couple of years ago! I run a decent size water chiller off-grid, to keep 13000l of water below ~21C in summer, in weather up to 42C. It is entirely doable.

PCM is a good idea to allow intermittent active cooling, and the more you insulate the coolroom, the better it will perform.

I'd seriously look at LiFePO4 rather than Lead-acid for your battery if you want to use one, as it is a lot more efficient that Lead-acid, meaning more available energy for pumping and cooling from your PV array in cloudy weather. It's also a good idea to significantly oversize your PV array, so that in marginal conditions you still have sufficient output, which will reduce the duration of diesel backup power operation.

Its a shaft driven Mono running off a Hino diesel engine. The absorbed power at 1200rpm is around 11kw. We need to plan to be able to pump at least 250kL a day.

Ouch... it should only take well under 5kW to lift 250000l per day up 40m, and send it through a properly sized (to minimise frictional losses) array of pipes, with a reasonably efficient pump. The actual rate of power to lift that much water 40m, run 24/7 is only about 1200W, but of course there are inefficiencies involved.

I'd probably aim to pump for say 8 hours per day (at ~30000lph) with a solar driven 3ph VFD, so that potentially you'd only need the battery for cloudy weather and night time coolroom operation in summer.

I'd probably look at something like a 15-20kW array, arranged to spread the peak output across the day (see the Virtual Tracker thread), rather than have a solar noon peak.

Gordon-Loomberah wrote:I'd probably aim to pump for say 8 hours per day

Generally the better average target is actually 6 hours.

I suspect the "11kw's" is the instantaneous power, so 11kWh's per hour when running, and is the effort of drawing it from a bore. Needing an approx 50kWh's of power per day to pump water allowing for some losses is not really surprising. Then supplying it at say 40m head pressure means more energy consumed than first meets the eye.

Why do you need a battery ?Its going to be more efficient (and a lot cheaper) to store water above ground than store electricity for the main pump.

Just oversize the pump so it goes like the clappers on sunny days, and at night or cloudy days, draw water from your above ground storage tank/pond.

As batteries are inevitably the most costly item in any off grid system, you can probably get by with a minimal sized battery just for some basic "system" power.

You would need to run some numbers, but for a cool room you could (?) " store cold" in the form of a few tons of ice.Chilling plants are often historically rated in "tons" which refers to the amount of cooling from the latent heat absorbed by the melting ice. Anything you can do that is really simple and reliable will beat bulk battery storage hands down.

Hi gfsben Great ideas given on here already !! I will follow it with interest and perhaps a comment or two.What temperature is the pumped water. Hot or cold ?? If cold it may be a substantial source of 'cold' for use in the cool room if below average ambient.I am too of the opinion that batteries for the main pumping may be unnecessary. Big tanks are cheap and do not wear out from cycling. The 40 meters given, is that the standing water level depth up to the surface/pump ?? what is the distance and height to pump the water then ? Any pressure required at the discharge, eg spray nozzles or just trickle ? I suppose we should ask the normal sun days and overcast days.

Thanks for the replies. Some great advice already. And thanks David for the extensive chat this morning. Confirms a lot of ideas and suspicions I had on the current proposal.

The consensus so far seems to be definitively against running the pump off a system that requires batteries. More efficient and more reliable to use a direct DC to variable frequency AC controller coupled to the pump/motor. A separate system could then be sized to cope with the cooling requirements (achievable in a number of different ways) and what ever else we may need and want in the future. - At the moment its only a couple of fridges, lighting and computer stuff, but we will be wanting to run other machinery, as well as hopefully converting our petrol powered cherry pickers to electric/LiFePO4 swap and go- recharged at the shed.

Gordon- I don't doubt that you have a system capable of running your chillers from batteries. But you still have to allocate battery capacity to achieve this, not to mention having functional batteries in the first place. If a slightly larger chiller is used, potentially itself running directly from PV similarly the the pump, then charging a large mass of water/coolant as sensible heat, or a bank of phase change packs as latent heat, then you have a much more passive and potentially much larger, cheaper and long lasting storage media.

On the pump- Its the static head plus line losses and back pressure due to the drippers. I did check the pressure at the bore pump while it was running and worked out it was effectively another 18m. So total head of about 58m.We have a number of small tanks on hills and stands scattered around the property, so domestic water is always on tap. Like I said, date palms are pretty tolerant of when they get water. Even a couple of weeks without a drink is not a big deal, so we are not going to go out of our way to run the pump from batteries or a generator, or get a tank that can store millions of litres. The shaft driven Mono 820 that we have is no doubt not the most efficient pump around. Especially when you take into consideration the losses in the belt drive and other bearings. We have every intention of upgrading to a centrifugal submersible at some point in time. The mono pump is just new now (we used to have a Mono 2521-now discontinued) and we have all the infrastructure to haul it out and service it (including replacing the stator), so I think we are going to give it a bit more of a go for now. The advice that I have had is that a PV to pump inverter, like from Lorentz, Franklin or JFY are quite suitable to running a normal 3 phase electric motor. So we could start off with that attached to the Mono 820, then later upgrade to a submersible if we want. (if we get sick of winching the mono out of the hole and the 12 lengths of pipe and shaft that go with it:)

So that would leave us requiring a separate smaller off grid system. I dont know much about SMA but I like the fact that Selectronic can be super reparable and that you can preemptively change the electrolytic capacitors. Also that it could use a 120V battery bank. We might ultimately want to use three phase machinery, but we could add inverters later when we do actually need it. Right now its just a little cool room and it sounds like a Selectronic 7.5kW could do that easy, even before I get around to thermal storage.

The batteries- I would still like to go Lithium but if the installer has no interest in them, then perhaps id capitulate and follow the line of least resistance- VLRA,Gel or flooded Lead. Id still advocate for a smaller bank than he quoted, especially since its wouldn't be covering any bore pump load.

Roughly what size PV array for the off grid/batteries? Around 8kw?

Am I getting closer to a good system? Should this be what I ask the installer/s for a quote on? I think we are pretty set on using local people. There is pretty good level of experience and capacity here given the population. They just might be a bit conservative in there approach. Which is understandable given the conditions and distances of the systems here.

Hi Jaahn,Water temp- its a good question. I have been asked it before and I have been meaning to get an accurate measurement. I know just generally that its not cold, I might even say its nearly tepid. So it wont work directly to cool the coolroom. It does raise an interesting possibility of using it on the condenser of a chiller, i think it would be cooler than the air in summer. Not sure it would be worth the complexity or plumbing though.